Portable devices, e.g., cell phones, pagers, laptop computers, personal digital assistants, and the like, may require accurate, stable, low-dropout regulated voltages to various sensitive load modules in such devices. Such load modules may vary with each device, but may include digital loads, analog loads, a reference oscillator, a real time clock, and/or the like. Such devices are typically powered by a battery, but may be powered with other voltage sources such as a solar source. Such power sources often provide unregulated voltage. A battery may provide a voltage source that varies considerably over its useful life and with the amount of load placed on it. When multiple batteries are used in series, such problems may be compounded. Thus, the various load modules in such devices typically cannot operate off direct battery voltage.
To condition an input voltage source and provide a regulated supply voltage to separate load modules in such devices, a low-dropout voltage regulator (LDO) is typically utilized. LDOs are typically integrated circuits that provide conditioned output voltages over varying loads with minimal voltage dropout over a relatively wide input voltage and operating temperature range. LDOs may provide a fixed output voltage or a varied output voltage. Other portable devices may have a power management unit (PMU) including one or more LDOs to condition an input voltage source and provide a regulated supply voltage to separate load modules and to provide other functionality.